https://publications.jrc.ec.europa.eu/repository/handle/JRC108181

Most relevant here is that they found significantly more caps than bottles, indicating that they get lost. Also lots of other single-use plastics there practically everything that can be avoided has been hit by the banhammer. Oh, cigarette butts I'd expect them to mandate those to be biodegradable in the future.

Things such as fibres from fishing nets and unidentifiable pieces of polystyrene and stuff of course don't get addressed by this, but that's not the point the point is to do what can be done.

One of the most important ones is this one: https://joint-research-centre.ec.europa.eu/jrc-news-and-updates/stemming-tide-beach-litter-2018-09-25_en

This was the basis for the decision to mandate the caps be attached to the bottles, since they found a lot of caps and less bottles. This would indicate a lot of caps get separated from their bottles, which this change should mostly fix.

The other was an interview with this guy: https://zwerfinator.nl/ I can't find the interview, no idea why, but he hasn't published the results yet (no idea why, it was scheduled to be published I think, but somehow got delayed). They were saying the new pfands really helped and the number of bottle caps have gone down. But this is highly depended on the location. For example a lot of research is focused on beaches, where there is obviously often a large delay between the deposition and the collection. In city centers this time is often much shorter, so the impact of changes are seen faster.

So sorry to disappoint, it's too soon for a peer reviewed study diving into this. Also with all the other changes the EU has mandated on litter and single use plastics, it would be hard to quantify which implementation has what effect.

But my thinking was: There is for me good data showing this is an issue (which I was doubting) and the solution seems solid enough. Other changes like pfands on small bottles and cans have made a big impact (research is available for this, for example https://open.overheid.nl/documenten/ronl-8b11214f23388b3395402609d76286475b4f2908/pdf). And the people doing the research say they've seen results that it works. So that was enough to convince me.

If somehow the caps being attached doesn't lead to less caps in litter, that would be a very interesting result. Without a doubt the EU would change the regulation to fix it, depending on why they think the change didn't work. But this would not lead to the caps being like they were in the past.

I can't find it on mobile right now. It was a preliminary result, because the attached caps haven't been required that long. Also most countries have implemented extra pfand systems for small plastic bottles, which also helps. So it's tricky to say which regulation helped most.

But there are plenty of sources of how many bottle caps there are in the streets and oceans. And how harmful they are to animals who think the small bright things are food.

It also makes sense, instead of the bottle and the cap becoming seperate pieces of trash, it's now a single piece. So it reduces the number of pieces if not the volume of trash.

Also for people from the US where bottles are shredded and caps typically not recycled. In Europe the caps also don't get recycled, but instead removed. The bottle is then checked for leaks and defects and if it passes it's cleaned and then reused. Actually recycling plastic is hard, so this way a bottle can be used at least two or three times.

You don't get your pfand in many cases if the cap isn't on, as well as the label many times. This isn't so much needed for the recycling but important for the whole process. For example groceries are required to take in bottles, but are allowed to limit this to bottles they sell. So the barcode om the label is checked for this purpose. The label is removed in the recycling process. The cap is required to motivate people to return those and not have them turn into litter. It's also a hygiene thing for the people handling the bottles, often there is liquid still in the bottle and without the cap it comes out during handling.

I will find the data later when I'm on desktop.

Im interested too on the data